Lithium ion conductors based on Li2M3+M4+P3O12 (M3+ = Cr, Fe, In; M4+ = Ti, Zr and Hf) have been synthesized. The Li2InTiP3O12 show larger conductivity (σ573 K, is 1.22 × 10 3 S cm-1) in the series of compounds under study and the results are discussed in terms of the polarizability of the network cation and the unit cell volume.